Your Magic will accept the SIM, but will only let you use their network if you unlock the phone, aka remove the carrier lock.

To obtain the code, you can attempt to wrestle Rogers to give it to you, but I doubt that they'll work with you.

The only option (I used this to use my Dream on Fido) is to purchase an unlocking code. I found a seller on eBay who did it for $5 in under 3 hours. Once I received the unlock code, I put in the other carrier's SIM card. Now, my Dream didn't automatically connect to a network. It stayed in Emergency Mode. I had to turn on the wireless manually. At that point, it asked for the unlock code.

Once that code is entered, you can take the phone to any carrier you desire, and swap SIM cards without any issue.